1. Field of the Invention
The present invention relates to an undercut-engaging dowel including an anchor rod having load application means at one of its end and a head, a diameter of which increases to a free end of the anchor rod, at an opposite end, and an expansion sleeve having a central bore through which the anchor rod extends, a circumferential groove, and a plurality of expansion tabs separated from each other by longitudinal slots and extending from the circumferential groove toward the head with the expansion tabs expanding radially, upon the expansion sleeve being displaced over the head.
2. Description of the Prior Art
In attachment systems, in which small spacing distances between axes and edges should be provided, form lockingly anchoring elements are used. In such systems, where spacing between the edges and axes is of a critical importance, in addition to anchoring of setbolts in structural components by casting them in a liquified mass which later solidifies, undercut formlocking means is used. When such attachment systems are used, an undercut-engaging dowel is anchored in a bore in which an undercut is formed by a special tool in the vicinity of the bore bottom. For anchoring the dowel, an anchor rod, together with an expansion sleeve mounted thereon, is inserted into the bore, and the expansion tabs of the expansion sleeve expand radially due to relative movement between the sleeve and the anchor rod. The expansion tabs, which expand into the undercut, form a formlocking connection with structural component.
An undercut-engaging dowel according to another embodiment does not require, for its anchoring, a preliminary formation of an undercut with a special tool. Rather, the dowel itself automatically forms an undercut upon being anchored. The formation of the undercut in this case is effected by rotation of the expansion sleeve while it is being driven, in the setting direction, over the widening head of the anchor rod by axial blows. The expansion tabs of the sleeve are equipped with cutters which form an undercut in a bore by milling or chiseling the bore wall. After the setting process has ended, the radially expanded tabs formlockingly engage the undercut formed in the bore. In addition to these undercut self-cutting systems, also known are undercut systems with which the undercut is formed without the expansion sleeve being rotated.
Undercut-engaging dowel, which is anchored in a preliminary formed undercut, has a very high resistance to displacement under a load and achieves, to the most possible extent, the carrying capacity of cast-in setbolt. Nevertheless, the expenses associated with anchoring of undercut-engaging dowels in bores with preliminary formed undercuts are rather high. The undercut self-cutting dowels such e.g., as disclosed in European Patent EP-B-O 217 053, have a noticeably smaller setting expenses. However, the resistance of these dowels to the displacement under load is very weak and approaches more to that of conventional forcelockingly anchored expansion anchors than to that of cast-in setbolts.
Accordingly, an object of the present invention is an undercut-engaging dowel having a resistance to displacement under load which approaches to that of a cast-in setbolt and at the same time can be formlockingly anchored in a structural component in a simple manner and without excessive expenses.